474 J. W. SPENCER — COVEY HILL REVISITED 



spring floods. This is a very common feature about small lakes, where 

 boulder beaches are raised several feet on the leeward side. 



Indeed, some shallow rock basins are due to ice expansion in crevices 

 and subsequent lifting of the loosened blocks, according to the theory of 

 K. Loranges.^ The creviced structure is favorable for this result, espe- 

 cially during changing levels of water, due to floods or the impeding or 

 opening of the underground drainage, which was observed as obtaining. 

 The theory of a pool beneath falls does not seem applicable to the forma- 

 tion of a pond situated at a distance from the head of the gorge. 



The time of the broad flood, sweeping through the depression behind 

 Covey Hill, was marked by the drainage from a large body of water, but 

 its duration may not have been long. Indeed, the conditions could only 

 permit of a relatively small snout of a glacier impinging against the 

 northern side of Covey Hill, with open water on the western side and a 

 district free of ice on the eastern. At the later date of the formation of 

 the Gulf the glacier was situated much farther away, as shown by the 

 traces of terraces on the northwestern side of the hill, being the same as 

 mentioned by Woodworth, at a corrected elevation of 915 feet above the 

 sea, corresponding to the floor of the outer valley at the head of the Gulf 

 proper. These features preclude the idea of a sweeping supply of water 

 from a glacial dam (which could not have been less than 1,025 feet above 

 the present sealevel) having formed the Gulf. 



Origin of Covey Hill Gulf 



i'rom observations in the field the conviction left is that Covey Gulf 

 was formed by the local drainage only since the time when the glaciers 

 left the upper part of the hill. What length of time has elapsed since 

 the ice epoch in this region? Difficulty is found in following and iden- 

 tifying the old shorelines north of the Adirondacks, although fragments 

 of beaches and deltas may be frequently seen. Their characteristics here 

 are unlike those of the Iroquois beach south of Watertown. x\fter allow- 

 ing for post-Glacial deformation, the height of the Covey Hill spillway ap- 

 pears to be 50 feet above the plane of Lake Iroquois, the outlet of which 

 was by the Mohawk Valley. Accordingly, with our present knowledge, 

 it would seem that the floods sweeping the channel came "from a glacial 

 lake of somewhat earlier date than the Iroquois beach, which bounded 



3 Geologiska Foereningens, Stockholm, 1874-1875, p. 343. My attention was called to 

 this theory for explaining certain shallow rock basins by Professor Broegger, who placed 

 high value on it. 



